Conventional telephone systems can provide a caller's status information, but do so in a costly manner that requires significant user time. For example, the office based PBX telephone system provides a caller with status information.
Determining whether the party's line is busy or available requires a caller's telephone to poll a central station and wait for a call back to receive status information.
At present, the telephone industry is in the process of switching to digital technology (i.e., Integrated Services Digital Network (ISDN), and Asymmetric Digital Loop (ASDL)). ISDN is an international communications standard for sending voice and data over telephone lines. ISDN technology transmits data at a rate far faster than prior telephone connection technologies. ISDN lines generally include three channels, two bearer (B) channels and one data (D) channel. Each B channel carries voice and data at a bandwidth of 64 kbps (thousands of bits per second), and the D channel handles signal control information. ISDN's two B channels enable the caller to simultaneously receive and send information. Currently, digitally enabled telephones are being produced.